A former NYPD cop who served more than a decade behind bars for killing an entire family in a notorious drunken car accident is now working as a janitor at a Catholic school on Staten Island.

Joseph Gray started Monday as a member of the maintenance staff at St. Clare’s, which sent a letter to parents explaining that it was hiring Gray because of a “faith of forgiveness and mercy.”

“Since the legal system is satisfied with Mr. Gray’s return to work, we believe he should be given the opportunity to do so,” the letter, signed by Monsignor Richard Guastella and Principal Jo Rossicone, reads.

Gray, 51, will be working part-time, during the afternoon, mostly cleaning up the cafeteria.

Gray’s blood-alcohol was twice the legal limit when he fatally mowed down pregnant Maria Herrera, 23, her son, Andy, and her sister, Delcia Peña, in August 2001 in Brooklyn.

Herrera’s unborn child died after being delivered by emergency C-section.

Gray had been boozing in the parking lot of his police precinct and then at a strip club before getting behind the wheel.